This invention relates to irrigation controls, and more specifically to control circuitry that is impervious to current surges induced by lightning strikes in the field wiring.
Irrigation systems such as, for example, sprinkler systems on a golf course, are often operated from a central location at which a complex computer- or microprocessor-driven control apparatus controls a large number of sprinkler valves out on the golf course.
Because the valve control wiring runs for considerable distances at a shallow depth underground in open terrain, it is subject to sharp induced current spikes or surges from lightning strikes in thunderstorm-prone areas. This does not normally pose a problem for the wiring and the valves in the field because they are sufficiently robust to withstand even a strong current surge for the few microseconds"" duration of a lightning strike. The problem arises, however, in the much more delicate electronics of the central control equipment, in which control transistors, circuit board traces, and other components can be damaged or destroyed by a strong surge in the few microseconds before protective devices can react.
The present invention protects the control electronics from lightning surge damage by electrically isolating the valve actuating circuitry from the control logic circuitry and configuring the actuating circuitry as a low-impedance path that is mechanically strong enough to withstand the power dissipation from a lightning surge in the few microseconds before a protective plasma device can fire.